Bone Swap
by KitCat97
Summary: My favourite trope with my favourite skele-bros. Enjoy this random body swap fic! .( u *).
1. Chapter 1

Papyrus woke slowly, blinking sleep out of his eyesockets and sitting up on the bed. He turned his head to where his action figures usually sat, only to find Sans' shelf full of joke books.

"SANS!" Papyrus shouted. "ARE YOU PRANKING ME ACROSS TIME AND SPACE AGAIN?" No response. Sans must have still been asleep.

Papyrus settled deeper into the cushiony surface of the bed to wait.

.(^u~*).

"on days like this, kids like you... should be burning in hell," the familiar beginning to a terrible nightmare snapped Sans awake. Usually when he awoke from one of those nightmares, his magic would be acting up, sending a blue glow through his semi-dark room. That wasn't happening. The room was bright, though a burnt orange glow touched the things nearest him. He sighed, leaning back against the pillow and rolling onto his side.

A table filled with action figures filled his vision. Sans shot upright with a strangled noise. He stumbled his way out of the race car shaped bed.

'seriously, what the hell is going on,' he thought as he walked out of the room towards his own room. He knocked nervously.

"papyrus?" Sans called his brother. The door flung open with a bang.

"SANS, FINALLY! WHAT'S GOING ON? WHY WAS I IN YOUR ROOM!?" Papyrus spouted out. Sans glanced down at his brother.

'wait a second...!' Sans yelped, catching his brother's attention.

"SANS?" Papyrus finally managed to flick the light on, flooding the shadowed hall with brilliant light.

.(^u~*).

"OH MY GOD SANS THERE'S A DOPPELGANGER HELP!" Papyrus yelled, stumbling backwards.

"what are you talking 'bout bro?" The clone asked him. Papyrus simply swung his arm to point at the other him who stood brazenly in his home.

The doppelganger froze, looking at the accusing finger, then trailing up the arm that held it.

"uh, bro, hate to burst your bubble, but you may want to look at the entire situation..." Papyrus simply stared hard at this invading copy before looking down at his own arm.

A bare bone. Further up, the end of a short, white shirt sleeve. No glove, no scarf tail. A confused 'NYEH' slipped out. He looked back at the copy.

"SANS?" Papyrus murmured. The other skeleton nodded.

.(^u~*).

Cliffhanger. I do have ideas to finish this. Dragging Alphys in for one!


	2. Chapter 2

A bare bone. Further up, the end of a short, white shirt sleeve. No glove, no scarf tail. A confused 'NYEH' slipped out. He looked back at the copy.

"SANS?" Papyrus murmured. The other skeleton nodded.

.(^u~*).

Papyrus looked like he had been slapped with a fish. He completely collapsed backwards with a strangled cry. Sans sighed.

"hey, bro, doesn't undyne have alphys' number?" Sans asked.

"YES," Papyrus said questioningly.

"i figure alphys might know what happened to us. let's go see undyne!" Sans cried. Papyrus leapt up from his spot on the floor.

"YEAH!" He shouted, charging towards the front door. Sans followed his brother, who knew the regular way better than he did. For once, Sans couldn't see any of his shortcuts. He supposed it had something to do with the switch.

.(^u~*).

Getting to the middle of Waterfall from Snowdin took longer than Sans remembered. Then again he usually took his shortcuts, so he didn't take long to get there usually.

Papyrus knocked decisively. The door creaked open, and Undyne poked her head out, looking half asleep.

"Hi Sans, Papyrus, what're you two doing here this early?" Undyne muttered.

"well, undyne," Sans said. "we don't have alphys' number, and we need her help today."

"Oh, that's an odd request Papyrus. Well, I guess I can call her for you. She should be here pretty quick, especially since the River Person usually parks near her place." Undyne said with her easy grin. She disappeared back into the house.

.(^u~*).

Alphys came running as fast as her claws could carry her. While she normally wouldn't go out of her way for something like this, Undyne, her not-so-secret crush, had been the one who called.

"U-u-undyne, I, uh, I came as s-soon as I could. W-what seems to be the problem?" Alphys stuttered out.

"Well, I, um, don't exactly know," murmured Undyne. "I called you because Sans and Papyrus came banging on my door and they both seemed pretty freaked out. That's what tipped me off that they needed some help. Sans is usually pretty unflappable, but he seemed the more freaked out of the two. The other thing is that Papyrus was a little quieter than usual." Undyne glanced back at her house. "Well, anyway, they're inside having some tea to calm down. Go on in."

Alphys nodded, skirting Undyne to go inside. The sight she saw was pretty unusual for the normally relaxed skeletons. Papyrus was worrying at the Rubik's cube she knew Sans kept to calm his nerves, while Sans was filling in a crossword with surprising speed, especially since the smaller brother usually handed them to Papyrus. Papyrus glanced up first.

"oh, hey alphys." Papyrus said*, making Sans look up from the crossword.

"THANK YOU FOR COMING SO QUICKLY ALPHYS!" Sans gushed, running up to her. Alphys flinched back.

"I-it was no problem S-sans. It's not like I had a-anything better to do anyway. S-so, what made you t-two call me?"

"well," Papyrus began. "for one thing, he's not sans. i am."

Alphys looked between the two brothers incredulously, and began to laugh uncontrollably.

"Y-you guys," she said, still giggling. "I know I've been m-more antisocial lately, but a prank isn't the way to get me out of my lab."

"ah, c'mon alphys. maybe you should give us a chance. we weren't trying to patella you to be more social, and it wasn't meant to be humerus." Papyrus said with a grin.

"OH MY GOD SANS NO!" Yelled... Sans?

Alphys was confused.

.(^u~*)

Hi, so, yeah. More of this. Honestly, I wasn't going to drag Undyne into their problems, but she kicked down my imagination's door and threatened it. My imagination is understandably terrified of someone who suplexes boulders for funsies.

*This scene was from Alphys' POV, so she thinks it's Pap when it's Sans!


	3. Chapter 3

Welcome, this is just a quick warning that this chapter dips a bit into darker territory (Sans gets pissed) and major head canons abound (Including W.D. Gaster, so if you don't know about him... Let's just say Undertale fanfics probably aren't for you, eh?). Other than that, enjoy~!

.(^u~*)

"OH MY GOD SANS NO!" Yelled... Sans?

Alphys was confused.

.(^u~*).

"B-but, wait, what, huh?" Alphys stuttered. "S-sans?" She questioned, pointing to who she thought was Papyrus. He nodded.

"What h-happened?" Alphys asked, flinching when the brothers turned their gazes on her.

"we don't know," Sans said.

"WE DID JUST WAKE UP LIKE THIS. IT WAS QUITE STRANGE," said Papyrus.

Alphys nodded thoughtfully.

"I'm sorry to say this, b-but, I don't know what happened. I-I don't think I could figure it out without my equipment either." Sans nodded.

"makes sense," he murmured. "well, let's go to your lab then!" Papyrus was quick to agree.

.(^u~*).

The skeleton brothers trailed after Alphys to the dock.

"Tralala," the River Person greeted them. "Where are you going today?"

"H-hotland please," said Alphys, and the River Person hummed as the three boarded.

"Tralala, words shape our world, so be careful what you say~," the River Person hummed mysteriously. The boat pulled up at Hotland dock. Alphys thanked the River Person, and they were on their way to the lab.

.(^u~*).

Alphys slid a key card through the scanner next to the door to unlock it.

"W-well, here we are," she said. "F-feel free to l-look around while I g-get the right equipment." With that, Alphys disappeared up the stairs.

Sans flopped into a chair, stretching out until his now-longer legs smacked against the table leg. He had less space than usual.

"seriously pap," he muttered in his brother's general direction. "how the hell do you manage being so frickin' tall." Sans continued on this vein of grumpy muttering until Alphys came back down with a device that looked like a cross between a barcode scanner, a laptop and a fax machine.

"A-alright," Alphys began. "I'm going to n-need you to stand exactly two f-feet apart, and then I'll activate t-the scanner." Papyrus and Sans complied. Alphys hit a button on the scanner.

Beeps and whirs filled the lab as the scanner did its job. A complicated series of images filled the screen, and the fax machine bit printed them out. Alphys would take the printouts off the machine almost immediately after they were finished, and scribbled notes on them in her nigh unreadable chicken scratch.

.(^u~*).

"W-well, I have, um, good news and b-bad news," Alphys said once the scan was finished.

"AND?" Papyrus said, looking at the scientist expectantly.

"T-the good news is that I should be able to figure out a way to get you back to normal."

"and the bad?" Sans asked.

"I s-still can't quite figure out what happened, since there's these weird s-symbols essentially etched onto your souls. I don't know what they mean, but I can tell that they're intrinsically c-connected to this problem, and that just getting rid of them wouldn't fix the issue, it would j-just k-kill you both. So I have to s-spend that much longer to t-translate and w-work around the symbols, rather than j-just erase them." Alphys said. "Although," she said thoughtfully, "these symbols k-kind of look l-like his notes. M-maybe I could check those!"

Sans blanched, somehow making his already pale bones even whiter. Neither Alphys or Papyrus noticed, both poring over the notes.

'if he is involved, there's probably no way we're gettin' back to normal.' Sans thought, grinding his teeth together with a slight growl. Burnt orange was starting to suffuse the harsh fluorescent lighting of the lab. A shadow formed behind Sans, the hovering demonic skull he summoned for battle. The mere thought of the prior Royal Scientist filled him with hatred and DETERMIN- the skull creature nudged his shoulder, making a whining sound that only he could hear, since it was still between worlds.

Sans could feel the rage drain away, along with the dangerous levels of DETERMINATION that had concerned the blaster in the first place. Sans looked back at the blaster he had inadvertently semi-summoned.

'ah, it's castellar, that explains why she stopped me," Sans thought, his snarl morphing into a faint shadow of his almost permanent grin. Castellar had been the first of his blasters that he had summoned, and had since then been very protective of him. The others, Century, Candara and Cambria, were slightly less protective, but still tended to stay pretty close.

'ah yes, speak of the devil,' Sans thought as the other three appeared to the same level as Castellar to nuzzle him. He rested his hand on Candara and then dismissed the blasters, considerably calmer.

Alphys and Papyrus didn't notice this interaction, still poring over the notes, Papyrus with his usual enthusiasm and Alphys with a careful touch.


End file.
